(1) Field of the Invention
This invention generally relates to the provision of an indication of a pressure loss. More particularly, this invention is directed to pressure loss indicators which may be employed for indicating the loss of pressure in pressurized gas cylinders or other pressurized containers. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
The present invention is particularly adapted for mounting entirely within a pressurized cylinder such as a fire extinguisher or a helium cylinder employed for inflating radar reflective balloons which provide a detection target for locating lost or disabled individuals in remote regions in emergency circumstances. Because in some applications a pressure loss of as small as 5% may result in insufficient gas being available to perform the intended function, a relatively compact, reliable and inexpensive pressure loss indicator is desirable from both a practical standpoint and (for many applications) from a safety standpoint. Accordingly, a general object of the present invention is to provide a new and improved pressure loss indicator having the foregoing characteristics. An additional general object of the present invention is to provide a pressure loss indicator which does not require modification of the wall or enclosure structure of the pressurized container and thus does not provide a potential additional leakage path.
(2) Description of the Prior Art
U.S. Pat. No. 3,910,223 discloses a device for sensing changes in pressure wherein a pair of chambers are separated by a membrane which carries a latch-operating ring. The operating ring engages a latch which normally prevents movement of a piston rod. One of the chambers is in fluid communication with a pressurized container in which the device is installed. A decrease of pressure results in unlatching of the piston rod so that the rod is displaced to an indicating position.
Devices which indicate a pressure loss or low pressure are also known in the art. U.S. Pat. No. 3,910,222 discloses the use of a membrane to divide a housing into a pair of chambers. A spring biased piston rod responsive to the position of the membrane energizes an audible alarm when the pressure of interest drops below a pre-determined level. U.S. Pat. Nos. 3,517,693, 4,232,698 and 4,297,687 disclose means for indicating low pressures in a gas cylinder. U.S. Pat. No. 2,798,449 and U.S. Pat. No. 2,967,509 disclose latch release means which indicate low pressure in a tire. U.S. Pat. No. 3,035,285 discloses a pressure responsive membrane which displaces a rod for releasing a reel having a line.